5.5.5 Shutdown Handlers

Applications have the option to let particular artifacts abort the shutdown sequence and/or perform a task while the shutdown sequence is in process. Artifacts that desire to be part of the shutdown sequence should implement the `griffon.core.ShutdownHandler` interface and register themselves with the application instance.

The contract of a `ShutdownHandler` is very simple

- `boolean canShutdown(GriffonApplication app)` - return `false` to abort the shutdown sequence.
- `void onShutdown(GriffonApplication app)` - called if the shutdown sequence was not aborted.

There are no default ShutdownHandlers registered with an application.